Tamperproof fuse and method of making same



Oct. 12, 1937. F. H. BussMANN TAMPERYPROOF FUSE AND METHOD OF MAKINGSAME Filed Feb. 20, 1936 l 1 f a ATTORNEY.

Patented Oct. l2, 1937 UNITED STATESv PATENT OFFICE TAMPEBPEOOF FUSE ANDMETHOD F MAKING SAME Frank H. Baumann, Richmond Heights, Mo.

Application February 2 0, 1936, Serial No. 64,806

' 19 claim. (ol. sot-119) Another object of my inventionis to provide arelatively simple fuse structure whose total cost l0 shall not beappreciably larger than most of those now in use and that shall betamper proof on the inside thereof.

In practicing my invention I provide a hollow body member for a fusehaving terminals thereon l and a fuse link therein. I further provide arelatively thin coherent coating of electric insulating material on theexternal surfaces of all electrically conductive parts inside the hollowbody and may also provide a similar coating on the inside surfaces ofthe hollow body.

In the single sheet of drawings,

Figure 1 is a view in section through a plug fuse of gonve'ntionaldeslgnembodying my invention, an

Fig. 2 is a view in section through La plug fuse of a somewhat differentdesign, also embodying my invention.

Referring first to Fig. 1 of the drawing, I have there illustrated afuse i I including a hollow body member I3, which is here shown as madeof porcelain such as is commonly used in fuses of this general design.although I do not desire to be restricted to this material nor to theexact form of structure shown as the principle embodied in my'ininvention can be applied equally well to other types of fuses. As isshown in Fig. 1 of the drawing, the body i3 hasa chamber I5 therein inthe usual manner.

The body i3 is provided with a centercontact il which may be in the formof a hollow rivet having a recess i9 therein in that end thereofextending in the chamber I5. A screw shell contact 2i is provided aroundan intermediate portion ofthe body I 3-a11 in a manner well known 1n theart.

A fuse element 23, which may include, in addi- 4 nected with the centercontact I1, as by a solder joint I1 in the recess I9.

After the fuse has been assembled thus far, I coat all of the surfacesof the exposed parts of the electric conductive -members inside the body5 with a relatively thin coating of an electric-in'- su'lating materialsuch as lacquer, varnish, shellac enamel or equivalent substances ormaterials. I may do this by spraying the electrically insulatingmaterial or compound into the interior of the 10' body, taking care thatnot only substantially all of the surface of the fuse element 23 butalso the exposed surfaces of center contact member I 1 and of shellcontact member 2i, spring 3i, heat coil 2l and the masses of solder 29,36 and 31 are 15 thoroughly -covered by this coating, which coat-A ingis indicated by39. It is obvious that at the same time substantially allof the inner surface of the walls of chamber i5 and of the auxiliaryvchamber 33 will also be covered, although this is 20 not essential tomy invention if the material of the body I3 is electricallynon-conducting. The layer on the inside surface of the body is alsoindicated by the numeral 39.

The fuse assembly may now be completed by 25 providing a transparentwindow 4I at the top and a closure cap 43, in a manner now well known inthe art. When the enclosure is in place, the electric conductive partsreferred to above as exposed are not accessible, but if the closure be30 removed or destroyed in whole or in part, as might be done for thepurpose of tampering with the fuse, these parts become exposed andaccessible, and where the expression "exposed" is used in thespecification and in the claims, it is to be inter- 35 preted as meaningexposed and accessible when there is an opening into the interior oi'thel fuse body.

While I have specifically mentioned the use of a spraying method toprovide the coating as above 40 set forth, I do not desire to be limitedthereto, since any other equivalent method effective for the samepurpose may beI utilized by me and among which methods may be mentioneddipping and brushing.

Referring now to Fig. 2 of the drawing, I have there illustrated asomewhat similar fuse assembly embodying a hollow body member 45 whichas shown consists of electric insulating material, such as porcelain.Here again, however, I do not desire to be limited to the use of this orof any particular material. The body 45 is provided with an internalchamber' 41 and the external Vsurface thereof is adapted to be engagedby and held within a suitable socket member.

supported by the body, a fuse link in the electrically connecting theterminals and a. relatively thin tough coherent electric-insulatingcoating adhering closely to and covering substantially all the surfacesof all the electricallyconductive parts of the terminals and the link inthe body, and to the inner surface of the 'hollow body.

8. A fuse comprising a. hollow body member, terminals supported thereby,a fuse link therein electrically connecting the terminals and' apaintlike covering of an electric-insulating material closely adherentto all electric conducting surfaces exposed in the interior of the bodymember.

9. The method ofrendering a fuse tamper proof which consists in coveringsubstantially all the exposed surface of the fuse link with a coherentand adherent electric insulating coating. l0. 'Ihe method of renderingtamper proof the inside of an enclosed fuse including electricconductive members in a body member, which consists in applying anelectric-insulating material to the exposed surfaces of all electricconductive members within the body to provide substantially allof thearea of such exposed surfaces with a relatively thin tough closelyadherent protective coating.

11. The method of rendering tamper proof the inside of an enclosed fuseincluding a hollow body member and electric conductive members therein,which consists in covering the exposed interior surface of the body andthe exposed surfaces of the electric conductive members therein with arelatively thin electric-insulating coating closely adherent theretoandv covering substantlally the whole area thereof.

12. 'I'he method of rendering tamper proof the interior of a plug fuseincluding a hollow body of electric-insulating material, terminalssupportedbythebodyandafuseelementlnthe body, which method consists lnapplying to the interior surface of the' body and the exposed surfacesof the element and of the terminals on the inside of the body arelatively thin tough electric-insulating` coating closely adherentthereto and covering substantially the entire area 4thereof 13. methodrendering tamper proof the interior of a plug fuse which method consists'inpalntingsubstantiallyallsurfaceareasofall'intheinsldeofthehueelectrically non-conbody.

ducting by the application thereto of a thin tough closely adherentcoating of electric-insulating material.

1,5. The method of rendering a plug fuse tamper prooi on the insidethereof, which method consists in preventing electrical connectionbetween its contact members and electrically conductive material whichmay be placed inside of the fuse to bridge the contact members thereofby `electrically insulating the surface areasy of substantially allelectrically conductive parts in the inside of the fuse.

16. The method of rendering a plug fuse tamper proof on the insidethereof, which method includes insulating by a coating of electricinsulating material substantially all electric conducting parts withwhich electric engagement is necessary to effect bridging the fuse byforeign electric conducting material which may be placed in the insidethereof.

17. The method of rendering a plug fuse tamper proof on the insidethereof, which method includes insulating by a relatively thin toughclosely adherent coating of electric insulatingmaterlalthesuriaoeofatleastthoseelectrlccou-l 'the inside of the fuse'.

18. A plug fuse comprising a hollow body member. contact terminalsthereon. a fuse link and electrical connections in the body normallymaintainlngthemsellnkinseriescircultwlththe contact terminals and anadherent covering of electric insulating material on atleast thoseportions of the electric conductlngparts which it is necessary to causeto be electrically engaged by foreign electric conducting material tobridge the contact terminals, when such foreign ele'ctric conductingmaterial is placed in the hollow body for the purpose of effecting suchbridslns.

19. A plug fuse comprising a hollowbody member, contact terminalsthereon, a portion of one ofsaidcontactterminalsboingexposedtotheinterior of said bodymember,- a fuse link in the body member, electricconnections normally maintaining the fuse link in leri circuit rela tionwith the contact terminals and an electric insulating coating on thesurface of at least those electric conducting parts ln the body, which,if uninsulated ,and mounted together with the otherpartsoftheelectricconductingmembersinlike manner in a like hollow bodymember and engaged by foreign electric conducting material inserted insaid like hollow body would cause bridsins of the contact i RANK H.BUBSHANN.

